Capillary transducer



Feb- 10, 1948. c. F. BURGESS CAPILLARY TRNSDUCER Original Filed Jan. 22, 1945 2 Sheets-SheI 1 Feb. 10, 1948. c. F. BURGEss CAPILLARY TRANSDUCER Original` Filed Jam.y 22, 1945 2 Sheets-Sheet 2 AMPL /F/Ef? Zzyen for Ressued Feb. 10, 1948 CAPI'LLARY TRANSDUCER Charles F. Burgess, deceased, late of Bokeelia, Fla., by Oliver Storey, Wheaton, Ill., trustee Original No. 2,416,978, dated March 4, 1947, Serial No. 573,913, January 22, 1945. Application for reissue August 8, 1947, Serial No. 767,600

9 Claims.

This invention relates to an electrical apparatus and more particularly toa reversible transducer for converting electrical energy into mechanical energy or vice versa. The invention in particular provides an energy-converting means which will convert electrical potential directly into liquid pressures or will convert liquid'pressures into electrical potentials.

At present, with one exception, electrical energy can be `converted into mechanical energy or vice versa only by .the use of solid materials. Thus magnetic or electromagnetic fields may act upon ferromagnetic materials or currentfcarrying materials. As a rule, this will result in forces being generated in a manner analogous to the action of two magnets. It is also possible to utilize the phenomenon of magnetostriction involving a lengthening of a ferromagnetic material. Apart Lfrom lthe action of a magnetic or electromagnetic `field, on a liquid carrying current, no ,direct `conversion of `energy between electrical or magneticl energy on one hand into mechanical energy onfthe other hand is possible with a liquid prior to this invention.

Similarly, electrostaticelds may be used .in connection with solid materials. Thus, `on the one hand, ythe tendency for two similarly charged particles to separate may be involved .in the movement of two conducting plates, .such as in the electrostatic typeof volt meter. In a piezo electric system, .the .stress in a crystal due to an electromotive force representsy an energy transformation. However, such forces are restricted to crystalline materials. There is no means known in whichpressure in a liquid and voltage in a circuit may be directly related to each other `as the two. parameters in a Etransducer system.

BY virtue of the invention herein, a new and different .energy converting cycle is possible and involves on the mechanical side the direct generation of hydraulic pressures. yA steady hydraulic pressure represents energy in potential form, while a varying hydraulic pressure is potential energy varying with time, and thus may represent power. It is believed that the invention herein described `is the ronlymeans `lnown wherein a direct relationship lbetween hydraulic pressure and electric potential is utilized in energy transformation. The transformation may proceed in either direction.

This invention utilizes a capillary .electrometer and provides a substantially incompressible mechanical coupling between I.the capillary meniscus and a point outside of the electrometer system.

Ihis outside point may have either a load or generator for mechanical forces coupled thereto. The electrometer of course has metallic circuit connections to the interface forming liquids. Thus the electrometer system may receive electrical energy from `an outside source and supply mechanical energy to the outside point or the operation may be reversed. Hence a true energy transfer from one system to another Inay be effected. Inasmuch as the energy transformation is eiected in the electrometer system as hereinafter described, it follows that this electrometer system is 4a transducer. A capillary electrometer involves the action of a liquid conductor and electrolyte -meeting in a, meniscus interface in proximity to an insulating surface so that capillary forces may exist. In its simplest form, a capillary electrometer comprises a glass tube having a capillary channel therethrough within which mercury and an electrolye, such as dilute sulphuric acid, meet to form an interface. Upon application of yan electric potential across said interface, a change of said interface will result. Conversely, vupon change of the interface, a potential will be generated. t has hitherto been customary to Drovide mercury or mercury-bearing substances as means for applying the potential to the liquids on opposite sides of an interface. While the fundamental nature of a capillary electrometer and its operation are still more or less obscure, it is believed that the interface behaves like a condenser in that current conduction does not ccur providing the applied potential is maintained below a predetermined threshold value. In the case of mercury and dilute sulphuric acid, the threshold value is approximately one-half volt, and voltages in excess thereof will have `deleterious results on the electrometer.

I1 the electrometer interface is considered as a condenser, calculations have shown that the capacitance thereof per unit area is extremely high in vcomparison to capacitances of conventional condensers.

The capillary electrometer has hitherto been utilized mainly as a volt meter wherein applied potential across the interface has resulted in interface movement unrestrained by external force. This movement was observed by a microscope or other means. While 4means for adjusting the `zero position of the interface have been shown in the literature, never before has a lcapillary electrometer had its structure changed so ythat true transducer action was effected. In order for true transducer action to may either receive or give vibratory energy. In

another form of the invention, the liquid or liquids making up the electrometer are utilized as part of the incompressible coupling. At any desired region where an electrometer liquid exists, a flexible wall or movable member may be provided. Between this member and the electrometer meniscus is an incompressible coupling in the form of electrometer liquid. The coupling communicates force between said movable or flexible wall and the electrometer meniscus. The movable or flexible mechanical member in contact with the electrometer liquid may provide a pressure communication between' the electrometer liquid and some outside system. The outside system may either be the seat of pressure generation or conversely may receive the pressures generated in the electrometer.

By virtue of this construction, it is possible to apply electric potentials across the interface and obtain mechanical responses available for use outside of the electrometer system. Conversely, it is possible to apply mechanical energy and introduce said mechanical energy into the electrometer system and use the potential generated across the interface.

By varying the energy, whether it be electrical or mechanical with respect to time, the converted energy-mechanical or electrical-will vary with time. Thus a conversion between electric power and mechanical power is possible.

While a single capillary electrometer represents a relatively feeble converting device, it is possible to provide a large number of such electrometers and thus, in the aggregate, handle substantial amounts of energy.

In a capillary electrometer. it is believed that the effective portion of the liquid interface, as far as electrometer operation is concerned, is adjacent the insulating solid surface. For this reason, a discrete interface has generally been formed in capillary bores. Such bores have generally been of the order of from ten microns to fty microns. Finer bores are undesirable due to erratic and secondary effects. Coarser bores in general lack sensitivity.

For a more detailed description of the invention, reference will now be made to the drawing wherein Figure 1 is an elevation cf a structure embodying one form of the invention. Figure 2 is an elevation of a modified construction. Figure 3 is a view showing a multi-unit system for handling substantial amounts of power. Figure 4 is a detail of a modified single capillary unit.

Referring first to Figure 1, container I of any suitable material such as glass may have open top II, vertical side I2, and bottom I3. Within container I0, there may be disposed a quantity of mercury I5. Wire I 6 of platinum or other suitable metal may be sealed into and pass through bottom I3 of the container to extend into the body of mercury I5. Ihus good electrical contact from the outside to mercury I5 is provided. Floating above mercury I 5 is electrolyte I'I, which may be any one of a number of materials that may be used in an electrometer. About ten or twenty per cent sulphuric acid is commonly used, although organic or inorganic materials for this purpose are well known. Thus aqueous solutions of the hydroxides of sodium or potassium, and aqueous solutions of the alkali metal halides have been used.

Container II] has glass tube I8 sealed into bottom I3 thereof, and extending up into the liquid above the level of mercury I5. Tube I8 has bore 20. Tube I8 ,itself may be any size desired and preferably should be heavy enough to withstand mechanical handling. Bore 2B may vary in range as hereinafter described. Tube I8 has bottom portion 22 thereof capped by member 23 of adjustable volume. In its simplest form, member 23 may consist of a piece of heavy rubber tubing closed at bottom 24 and telescoping over bottom end 22 of glass tube I8. The volume of member 23 may be Ycontrolled by clamp 2&3 and screw 2T. Member 23 is filled with mercury 23, which mercury extends up into bc-re 2E). The mercury in bore 2B is adjusted so that meniscus 33 is preferably slightly above the level of mercury I5. However, this is not critical and the level of meniscus 33 may be set at any desired point. Electrolyte il is disposed within bore 2i) so that meniscus 3) forms an interface between mercury and electrolyte. Member 23 is stiff enough so that, once adjusted, its volume remains constant in spite of electrometer operation.

In order to provide for a capillary space in the region of meniscus 30, a rigid member, here shown as needle 32, may be extended down into bore 2li in contact with interface 30.

Needle 32 must extend down into the mercury column sufciently so that an annular mercury meniscus is formed. The material of which needle 32 is made may either be insulating or conducting. If of insulating material, it may be formed of glass or other similar material. If needle 32 is of conducting material, it may be formed of platinum or other suitable polarizable metal. When needle 32 is of conducting material, proper adjustment of the needle tip may be necessary. The correct adjustment may be obtained by varying the needle position and operating the electrometer. When the needle is correctly adjusted, some polarizing film is formed, since no short circuiting of the interface results. When a conducting needle is correctly adjusted, the conducting nature of the needle is of no significance, and the needle merely provides a mechanical coupling from the meniscus to a point outside of the system.

The diameter of needle 32 is such that the difference in diameter between needle 32 and bore 23 at interface 30 provides an annular capillary region. This capillary region may vary within wide limits. The difference in diameter may be of the order of aboutone millimeter although this may vary widely. Thus, a capillary region between opposed insulating surfaces of needle 32 and inside Wall of bore 20 will be formed.

Needle 32 forms a rigid coupling between interface 3B inside of the capillary electrometer system and a point outside of the entire system. In order to terminate needle 32 in either a load or a generator, it may be fastened to diaphragm 33. It is understood that, instead of diaphragm 33, any other energy absorbing or energy generating means may be used.

To complete `the electrical circuit across interface 30, wire 36 may pass through sealed bottom '24 ofmember 23 and extend into the mercury Wires |6 and 36 may be connected to primary 40 of transformer 4| whose secondary 42 may be connected in any suitable fashion.

`If the capillary electrometer -system is to convert mechanical energy into electrical energy, a vibration generator is necessary at the free end of needle 32. Mechanical vibrations at needle 32 will change meniscus 30 to generate potentials across the interface. These generated potentials are conducted to primary 40 of transformer 4| and potentials induced in secondary 42 may be amplified or may be utilized directly in some load. Conversely, if reverse action is desired, secondary 42 would be supplied with varying potentials and thus function really as a primary. Winding 40 would have induced therein potentials which would be applied across interface 30 to cause movement thereof. The resulting movement would vibrate needle 32 and thus affect diaphragm 33.

Referring now to Figure 2, a modified structure is shownwherein the liquid in the electrometer is utilized as the incompressible coupling between the capillary interface and a point outside of the electrorneter system. Thus container 60 may have open top 6I and, as before, may have bottom layer 62 of mercury and supernatant layer 63 of electrolyte. Lead B4 may be sealed in the bottom of container B and contact mercury 62. It is understood that container Si) may be made of glass or any other insulating material. Tube B5 may be sealed to container 60 and extend up inside thereof through the bottom. yTube 65 has capillary bore 66. Capillary bore 60 may vary in size over wide limits between ten microns and one or more millimeters. `The length of capillary E5 may vary, although lengths of the order of between one quarter of an inch and three-quarters of an inch may be used successfully.

Tube G5 has upper end 10 above the level of mercury 62 and is open to electrolyte 63. The bottom of tube 65 may have attached thereto rubber tubing 12 whose free end 13 may be sealed in any suitable fashion as by glass stopper 15. Passing through stopper 15 and inside'of rubber tube 12 is wire 1. The inside of rubber tube 12 is lled withmercury 80, said mercury extending well up in bore E6. Electrolyte 63 eX- tends down bore B5 to form interface 14 with mercury.

The liquid column between the interface and rubber tube 12 is substantiallyincompressible and provides a connection between the interface and the wall of said rubber tube. Rubber tube 12 l A6 thisl value is ofthe order of about one-half volt per interface. In many instances, it may bedesirable to generate or respond to higher voltages. It is therefore understood that discrete globules of mercury and electrolyte `may be disposed in capillary 56 to build up as many interfaces as may be desired. Itis also possible to parallel two or more electrometers so that currents rather than voltages are added. ABecause of the similarity invactionbetween an electrometer and a condenser, there will be charging and discharging currents present. In order that substantial amountsof power; may be handled, it is possible to provide a composite system wherein a number of electrometers in parallel form a group, and a plurality of such groups may be operated in series.

Thus referring to Figure 3, a ypower unit is shown having a substantial number of parallel capillary elements to form a group and lseveral (here shown as two) groups in series. Each group may consist of an insulating block |00 having a number of parallel capillary passages therethrough. kThus block |00. may be a short cylinder having top and bottom faces |0| and |92. Capillary passages |03 may extend through from one face tothe other. Block |00 may be'of glass, polystyrene, Bakelite or any insulating material immune to attack by the electrolyte used, as

dilute sulphuric acid. The passages may be drilled, formed when block |00 is softened by heat or any other way. The spacing between adjacent bores should be as small as possible. The diameter of the bores may vary depending upon the process used. Bores of the-order of .l

millimeter may be obtained by molding glass or other thermoplastic insulator around a group of spaced wires. The wires may then be removed by dissolving with suitable chemicals.

Two blocks |00 and |05 may be provided with capillary Abores. The length of each'block may vary. However, the length may advantageously be of the order of one quarter to three quarters of an inch. Each bore preferably'has at least two interfaces formed by a globule of electrolyte between mercury columns. Thus a clean block may be dipped into mercury to force some up into each bore. Then the block may have one end dipped into electrolyte, under pressure to force some ,electrolyte up. Thereafter, a mercury treatment may follow.

Each bore may have as many cascaded interfaces as desired, it being understood that subforms the boundary between the outside and the electrometer system itself. In order to provide means for transferring energy from the liquid column to the out-side, rod 80 may be cemented to spot 8| on rubber tube 12. The remaining portion of rubber tube 12 is restrained by rigid covering 83 which, in its simplest form. may consist -of metal. The Volume of rubber tube 12 may be adjusted by clamping screw 84.

Wires 64 and 11 may be connected as in Figure 1. It is clear that, upon application of potential across the interface, movement of meniscus 14 will result in movement of the flexible wall portion and rod 80. The reverse action may al-so be obtained.

As hereinbefore pointed out, every interface has some threshold Voltage below which it is necessary to operate for proper electrometer action. In `the case of mercury and dilute sulphuricacd,

stantially all bores in one group have the same number of interfaces. Because the electrolyte generally has a higher electrical resistance, it is preferred to keep the electrolyte used to a minimum. Hence, there will generally be an even number of interfaces per bore. Thus a single block may have one hundred bores with four interfaces per bore. With two groupsin-series,

this would result in a four-volt threshold voltage.

The parallel capacitance will result. in a substantial value so that, under certain conditions, heavy currents may flow. f

Blocks 00 and |05 may be mounted in line with each other and have a casing |01 surrounding both. Casing |01 may be of the same material as blocks |00 and |05 and rmly joined thereto. Above block |00 is space |09 containing mercury ||0. Similarly, space between blocks |00 and |05, may be filled with mercury I I2. Below block 05 is space I-3 filled with mercury ||4. vItis understood that the capillary bores through each block form the sole liquid paths between the regions at the ends ol' each block.

One end of casing ||i1 may be sealed as at IIS. Conductor II'I may be sealed into the casing to make Contact with the mercury. VConductor IIB may be sealed at the other end of the casing. Thus, the two terminals will be Wires |'I and I I8. The bottom of casing |01 may be formed as flexible wall |20. Thus wall |20 may be formed oi steel sealed at the edge to the material of casing IDT.

Hydraulic pressure may be transmitted through flexible wall |29. the system will b e flexible wall |28 and the remainder of casing Ill?. Casing |01 may be fastened in position so wall |28 may work against a load or be actuated by a load. Air space |2I at the rigid end of the system may provide a restoring force and take up liquid expansion with temperature rise.

The action of the restoring force is not the same as in a simple mechanical spring system. In a capillary electrometer, when an interface has been moved in response to a potential, there is a tendency for the interface to remain in the moved position unless electrical conditions are also permitted to reach a new equilibrium. Conversely, if an interface is moved as a result of mechanical forces and the forces removed, the interface will tend to remain in the same position unless the electrical system can come to a new equilibrium. Gradually, over a period of some hours, the interface will return to a position of complete electrical and mechanical equilibrium due to surface leakage along the insulating container. Hence, any mechanical restoring force provided must be considered not as a complete restoring force for the entire system, but only for the mechanical portion thereof.

While theoretically, it would be desirable for each block to have the same number of capillary bores, in practice, this may be difficult to achieve under certain manufacturing conditions. As long as the number is approximately the same, one

grou-p will adapt itself to the remaining groups and the entire unit may operate. It is obvious that the number of capillary bores that may be paralleled in one group has no definite limit. Similarly, any number of groups may be put in series. parallel with each other, so that electrically they are connected together but physically and mechanically they may be separate. Thus heavy charging and discharging currents may impose a practical limit to the number of capillary bores in one group so that, under certain circumstances, it may be desirable to parallel groups.

Inasmuch as each electrometer unit is mechanically and electrically discrete, it follows that a plurality of such units may be connected electrically in series and mechanically in parallel or electrically in parallel and mechanically in series. Thus, the electrical series and parallel connections are obvious and would be the same as connecting other devices such as batteries in series or in parallel. Mechanically, a parallel connection would involve a plurality of units connected to one push rod so that each unit actuated the push rod directly. A series mechanical connection would have one unit operate upon another unit and finally the end unit operate on a load.

Thus, the disposition of the two blocks in Figure 3 constitutes both an electrical and mechanical series connection. It is clear that the series mechanical connection isnot necessarily in- The mechanical terminals of It is also possible to dispose kgroups in I 8 herent in the series electrical connection. Simllarly, the disposition of a plurality of bores through one block constitutes a parallel connection both electrically and mechanically. Again, the parallel electrical and mechanical connections are not necessarily interrelated.

In Figure 4, a detail of a structure is shown wherein the mechanical coupling between the outside and the electrometer system is applied at or near the portion of the system containing the meniscus. Thus capillary |20 may have at least two interfaces |30 formed therein. The remaining portions oi the electrometer system may be as shown in Figure l or Figure 2. However, it is understood that the mechanical energy coupling point in these ligures is not included. At point |31 on the outside of capillary |20, rod |32 may be rigidly connected. Rod. |32 may go to some load or generator for handling vibratory energy. By maintaining the rest of the electrometer system rigid, deiiections of capillary |20 at point IBI will result in transducer action. '-It is understood that capillary |29 would have walls thin enough for this purpose. Whether the coupling point between rod |32 and capillary |29 is in line with an interiace or not is of no great consequence.

By virtue of the invention herein, a simple transducer for reversible conversion of energy between ele'ctrical and mechanical is provided. The mechanical energy is in the form of pressure in a liquid and, as such, may be converted by mechanical means into movement of a mechanical member, By the use of a number of capillaries in parallel, the current handling ability or pressure in a liquid may be increased. By providing a plurality of cascaded interfacesl either in one capillary bore or a plurality of cascaded capillary bores, the potential handling ability or amplitude of a pressure wave may be increased. By combining these two modifications, it is possible to provide a transducer which can handle substantial amounts of energy or power.

The simplicity of such a transducer, together with the direct generation of pressure in a liquid, make it desirable for use in many fields. Thus the transducer may operate in connection With sound transmission between sound waves and corresponding potentials. Other fields of use may be in the detection of minute pressure waves such as exists in seismographs, thickness gauges, and other similar devices. A particularly desirable field for use resides in the generation of potentials corresponding to pressure waves in Various portions of living bodies such as, for ein ample, in electric cardiographs and sphygmomanometers.

What is claimed is:

l. A transducer comprising a capillary electrometer, said electrometer including two liquids forming at least one interface therebetween, means for establishing electrical connections to said interface'dorming liquids, a substantially incompressible connection from said interface, said incompressible connection going to a point outside of said electrometer system, means at the outside end of said incompressible connection for transmitting vibratory forces between a driven or driving means on the one hand and electrometer interface on the other hand, said means and .incompressible connection transmitting vibratory energy from said means to said interface or from said interface to said means depending upon the direction of energy conversion and circuit connections to said electrical connections for coupling a potential generator or load.

2. A transducer comprising a hydraulic system containing at least two different liquids, said system including at least one capillary bore with said liquids meeting in at least one interface to form a capillary electrometen means for establishing electrical connections to theliquids on opposite sides of said interface, said system including as a part the'reof a flexible wall portion, and mechanical means at said wall portion lli coupled thereto, said electrical conducting means to said rod and an electric circuit including said interface.

4. A transducer comprising a capillary electrometer including two liquids meeting to form an interface, a rod extending from said interface to a point outside of said electrometer system, said rod having a portion forming part of a capillary region within which said interface is located, vibration responsive means coupled to said rod and an electric circuit including saidv interface.

5. A transducer comprising an insulating tube, mercury and an electrolyte in said tube forming an interface, a rod extending within said tube near said interface to a point outside of said tube, said rod and the bore of said tube being so proportioned as to create 9, capillary annulus at said interface, mechanical means connected to said rod outside of said tube and circuit means including said interface.

6. A transducer comprising a tubular system including a capillary bore, said system having therein two liquids forming an interface in said capillary bore, circuit connections to said interface forming liquids for providing a capillary electrometer, said tubular system including at least a part thereof having a flexible wall and mechanical means on the outside of said tubular system coupled to said wall, said mechanical means being adapted to either receive or generate vibratoryV energy and said circuit connections being adapted to supply or receive electric potentials.

'7. An energy converting device comprising a sealed container lhaving mercury and an electrolyte therein, at least one block of insulating material in said container, said block forming a wall across said container to divide the same into two chambers, said block having a plurality of capillary bores connecting said chambers, said liquids being so disposed in said container and capillaries as to create at least one interface in each capillary, said container having a flexible wall as a part of one chamber for transmitting pressure between one chamber and a region outside of said container, electric circuit connections from the outside of said container passing through the walls thereof to said liquids whereby potentials may be applied across said interface or, if generated, said potential may be conducted to the outside, and mechanical means in said other chamber tending to exert a restoring force to the liquids in said container.

8. The structure of claim '7 wherein said container has at least two blocks spaced from each other to form chambers on each side of each block, the capillary bores in said blocks connecting said chambers in succession.

9. The structure of claim 1 wherein a hermetically-sealed container is provided for the capillary electrometer, said sealed container having a compressible gas in one part thereof. K

OLIVER W. STOREY, As Trustee for the Partnership of 0. W` Storey and Associates, Assignee of Charles F. Burgess,

Deceased.

REFERENCES CITED FOREIGN PATENTS Country Date Denmark A- Sept. 11, 1911 Number 

